In the semiconductor process, integrated circuits are fabricated on a semiconductor wafer. Semiconductor wafers can be stacked or bonded on top of each other to form what is referred to as a three-dimensional (“3D”) IC. Some semiconductor wafers include micro-electro-mechanical systems (“MEMS”), which is the technology of forming micro-structures with dimensions in the micrometer scale (one millionth of a meter). Typically, MEMS devices are built on silicon wafers and realized in thin films of materials.
MEMS applications include inertial sensors applications, such as motion sensors, accelerometers, and gyroscopes. Other MEMS applications include optical applications such as movable mirrors, and RF applications such as RF switches and resonators. MEMS devices introduce their own unique requirements into the integration process, however. Electrically interconnecting MEMS devices is an area of unique challenges.